A steam turbine, an example of a heat engine, normally includes an inner case accommodating a turbine rotor and an outer case accommodating the inner case. In the steam turbine, high-pressure steam is introduced into the inner case through a steam inlet disposed on the outer case. In the inner case, the introduced high-pressure steam is injected at a high speed, and this steam force applies a rotational force to a plurality of turbine stages of a turbine rotor to rotate the turbine rotor. The high-pressure steam having applied a rotational force to the turbine stages moves from an upstream side toward a downstream side through the turbine stages with its temperature and pressure decreasing, and flows out through an exhaust outlet.
Meanwhile, Patent Document 1 discloses a steam turbine including high-pressure and mid-pressure stages. As disclosed in Patent Document 1, this steam turbine includes a high-mid pressure integration dummy ring between a high-pressure stage and a mid-pressure stage, and a ring-shaped partitioning plate disposed between the high-mid pressure integration dummy ring and an outer case (outer turbine casing). The ring-shaped partitioning plate separates and protects an inner case (inner turbine casing) from mid-pressure steam having a high temperature, and thereby it is possible to reduce thermal stress of the inner case and to reduce stress of bolts fixing the inner case.
The inner case has a structure that is dividable into an upper part and a lower part having butting surfaces which extend in a horizontal direction on rim portions. The upper part and the lower part are fastened with a plurality of bolts to be fixed integrally while the respective butting surfaces of the upper part and the lower part are in contact with each other. The outer case has a configuration similar to that of the inner case.